New issue 2683: Infinite traceback with greenlets
https://bitbucket.org/pypy/pypy/issues/2683/infinite-traceback-with-greenlets
Antonio Cuni:
Consider the following minimal example:
```
import traceback
import greenlet
def run_in_b():
print 2
A.switch()
print 4
def run_in_a():
print 1
B.switch()
print 3
A = greenlet.getcurrent()
B = greenlet.greenlet(run_in_b)
run_in_a()
traceback.print_stack(B.gr_frame, 10)
```
On CPython, it prints simply this:
```
$ python hangs.py
1
2
3
File "hangs.py", line 6, in run_in_b
A.switch()
```
On PyPy, there seems to be an endless cycle of frames:
```
$ pypy hangs.py
1
2
3
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 190, in
_greenlet_start
res = greenlet.run(*args, **kwds)
File "hangs.py", line 6, in run_in_b
A.switch()
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 53, in switch
return self.__switch('switch', (args, kwds))
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 92, in __switch
args, kwds = unbound_method(current, *baseargs, to=target)
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 190, in
_greenlet_start
res = greenlet.run(*args, **kwds)
File "hangs.py", line 6, in run_in_b
A.switch()
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 53, in switch
return self.__switch('switch', (args, kwds))
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 92, in __switch
args, kwds = unbound_method(current, *baseargs, to=target)
File "/home/antocuni/pypy/default/lib_pypy/greenlet.py", line 190, in
_greenlet_start
res = greenlet.run(*args, **kwds)
File "hangs.py", line 6, in run_in_b
A.switch()
```
This is a minimal example which shows the issue; however, the bug causes issues
also with eventlet, in which `get_hub().run` plays the role of `A` and an
arbitrary `spawn()`ed function plays the role of `B`.
Tested with pypy 5.9 and nightly.
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